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A Crystallographically Oriented Intergrowth of Siegenite (CoNi2S4) and Millerite from the Morokweng Impact Structure, South Africa: Chemistry, Texture, and Origin

2018; Mineralogical Association of Canada; Volume: 56; Issue: 5 Linguagem: Inglês

10.3749/canmin.1800007

1499-1276

C E Beckett-Brown, Andrew M. McDonald, William Zhe,

Crystal Structures and Properties

Research Article| September 01, 2018 A Crystallographically Oriented Intergrowth of Siegenite (CoNi2S4) and Millerite from the Morokweng Impact Structure, South Africa: Chemistry, Texture, and Origin Christopher Edward Beckett-Brown; Christopher Edward Beckett-Brown § Harquail School of Earth Sciences, Laurentian University, Sudbury, Ontario P3E 2C6, Canada § Corresponding author e-mail address: ce_beckettbrown@laurentian.ca Search for other works by this author on: GSW Google Scholar Andrew M. McDonald; Andrew M. McDonald Harquail School of Earth Sciences, Laurentian University, Sudbury, Ontario P3E 2C6, Canada Search for other works by this author on: GSW Google Scholar William Zhe William Zhe Harquail School of Earth Sciences, Laurentian University, Sudbury, Ontario P3E 2C6, Canada Search for other works by this author on: GSW Google Scholar The Canadian Mineralogist (2018) 56 (5): 705–722. https://doi.org/10.3749/canmin.1800007 Article history first online: 02 Nov 2018 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Christopher Edward Beckett-Brown, Andrew M. McDonald, William Zhe; A Crystallographically Oriented Intergrowth of Siegenite (CoNi2S4) and Millerite from the Morokweng Impact Structure, South Africa: Chemistry, Texture, and Origin. The Canadian Mineralogist 2018;; 56 (5): 705–722. doi: https://doi.org/10.3749/canmin.1800007 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyThe Canadian Mineralogist Search Advanced Search Abstract The rare thiospinel siegenite (CoNi2S4) has been found in drill-core samples of quartz-norite as primary oriented intergrowths in millerite from the Morokweng impact site, South Africa. The mineral occurs as elongate, sub-parallel grains (10 × 50 μm on average, up to 100 × 500 μm) that are light purple under reflected light. Quantitative reflectance data compares well to current data sets and shows little variation among other Ni-Co thiospinel endmembers. The average major element chemistry of siegenite (n = 19) includes (wt.%): Fe 1.69 (0.65–2.99), Co 12.46 (7.92–15.72), Ni 43.84 (39.29–47.68), and S 41.90 (41.25–42.26), corresponding to the average formula (Co0.64Ni0.28Fe0.09)Σ1.01Ni2.00S3.98 (based on 7 atoms per formula unit). Laser-Raman spectroscopy along with single-crystal X-ray diffraction results supports the space group assignment, with no evidence to suggest a phase transformation. The X-ray diffraction data also support the inverse cation distribution for siegenite. Electron backscattered diffraction (EBSD) indicates that the siegenite (sgn) and millerite (mlr) are present in one of two possible crystallographic orientations (shared plane, orientation of plane): (1) (100)[012]mlr||(111)[10]sgn or (2) (001)[10]mlr||(110)[11]sgn. Further examination with EBSD suggests that the siegenite is twinned on {111} forming simple lamellar twins. Based on the data presented, it is suggested that the sequence of crystallization was millerite → siegenite → chalcopyrite, initiated by nucleation of Ni1–xS (millerite, at high T) and followed by the formation of siegenite between 356 and 282 °C which crystallized alongside metal-deficient Ni1–xS. This process caused the co-crystallization of millerite and siegenite, forming the oriented crystal-controlled intergrowth observed in the Morokweng quartz-norite impact melt sheet. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.